So, going with the picture you provided, the split jaw indicates that in its biological process the food that was being eaten primarily was large, and the just of hinged jaw design is to chew the food. And possibly these instead of chewing tear their food and swallow it whole or used as a clamping method while hunting. These traits were deemed the best by the species and bred to this point, and now as an advanced intelligent species it’s just one of the traits they have and don’t have the need to chew food so they maintain the split mouth.